Ca4-16 is without doubt showing a 'feathered mountain' at left:

Ca4-14 Ca4-15 Ca4-16 Ca4-17 Ca4-18 Ca4-19

The number of 'feathers' (7) and the ordinal number (16) indicates the moon, not the sun.

When classifying glyphs according to types I had difficulties with the type of sign at left in Ca4-18, but in the end I decided to define it as a variant of mauga. 'Feathers' on both sides should qualify the sign as mauga, while 'feathers' on only one side would put the glyph in the tapa mea group. Classifying glyphs has nothing to do with their meanings.

The three pairs of glyphs above suggest the left part in Ca4-18 is a sun 'mauga'. 18 is the sun equivalent of 16 in the meaning of maximum ('full sun' respectively full moon). 19 respectively 17 suggest decline has began.

There are 7 'feathers' in Ca4-16 and 6 + 5 = 11 in Ca4-18, both odd (and therefore 'bad') numbers. Probably we should add 7 + 11 to reach the even number 18. By this operation a message of 'moon' (7 in Ca4-16) will be integrated into the main subject, viz. the sun and its 'seasons'.